This disclosure relates to a cutting insert, a tool holder, and a tool comprising said cutting insert and said tool holder. The tool is a tool for machining a workpiece. More precisely, it is preferably a turning tool comprising a tool holder and a cutting insert which can be exchangeably fixed to the tool holder. The cutting insert can be fastened to the tool holder with the aid of one or more fastening elements.
Turning tools comprising exchangeable indexable inserts are already known in a variety of different designs. An example of turning tools of this type are long-turning tools, which are used in so-called long-turning lathes or long-turning automatic screw machines.
Traditional long-turning lathes are controlled mechanically via preset cams. Modern long-turning lathes are controlled by means of CNC technology via computers. For these modern, computer-controlled long-turning lathes, a variety of turning tools with exchangeable indexable insert exists.
The traditional, cam-controlled long-turning lathes are likewise still very widespread, however, and continue to be used in practice. For instance, in the manufacture of very small or precision parts, as are required in the watchmaking industry, cam-controlled long-turning lathes continue to be employed. However, the number of tools which are suitable for this is rather limited. This is mainly due to the fact that, for applications of this type, very small dimensions of the tool shank are necessary. As a rule, tool holders having a cross-sectional size of maximally 6×6 mm are suitable for the purpose. This, in turn, places particular requirements on the interface between tool holder and cutting insert, and on the overall stability of the tool. Moreover, in the production of very small, precision components, as are used in the watchmaking industry, an exact, repeatable accuracy in respect of the tools is crucial. To be able to ensure this in combination with the relatively small dimensions which are to be obtained and with a still guaranteeable mechanical stability of the tool is a major challenge from a design aspect.
Examples of turning tools which can be manufactured with very small dimensions and are suitable in the production of miniature parts for the watchmaking industry are known from EP 1 617 963 B1, EP 1 368 149 B1 and from EP 1 189 719 B1.
In these tool examples, the interface between cutting insert and tool holder comprises a ribbed structure, on which the cutting insert and the tool holder touch. This type of interface has several drawbacks, however, with regard to stability and precision. On the one hand, the forces which act in the axial direction or longitudinal direction of the tool are diverted into the tool holder via the screws by which the cutting insert is fastened to the tool holder. This results in a relatively high load upon the screws and a lower positioning accuracy. Furthermore, the ribbed structure is mostly arranged as a sintered and non-reground, i.e. ‘as sintered’ structure, which, in turn, adversely affects the positioning accuracy.